Basic XPS Information Section

The Basic XPS Information Section provides fundamental XPS spectra, BE values, FWHM values, BE tables, overlays of key spectra, histograms and a table of XPS parameters.
The Advanced XPS Information Section is a collection of additional spectra, overlays of spectra, peak-fit advice, data collection guidance, material info,
common contaminants, degradation during analysis, auto-oxidation, gas capture study, valence band spectra, Auger spectra, and more.
Published literature references, and website links are summarized at the end of the advanced section.
 Periodic Table – HomePage                     XPS Database of Polymers                    → Six (6) BE Tables



Gallium (Ga)

 

Gallium melts in your hand – Gao Gallium – Gao Bauxite – Gao metal is trapped inside Bauxite

 

  Page Index
  • Expert Knowledge & Explanations


Gallium (Gao) Metal

Peak-fits, BEs, FWHMs, and Peak Labels


  .
Gallium (Gao) Metal
Ga (2p3/2) Spectrum – raw spectrum

ion etched clean
Gallium (Gao) Metal
Peak-fit of Ga (2p3/2) Spectrum
(w/o asymm)


 Periodic Table – HomePage  
Gallium (Gao) Metal
Ga (2p) Spectrum –
extended range 
Gallium (Gao) Metal
Peak-fit of Ga (2p3/2) Spectrum (w asymm)

 .

Gallium (Gao) Metal
Ga (3d) Spectrum
Gallium (Gao) Metal
Peak-fit of Ga (3d) Spectrum (no asymm)
 

 

Survey Spectrum of Gallium (Gao) Metal
with Peaks Integrated, Assigned and Labelled


 Periodic Table 

XPS Signals for Gallium, (Gao) Metal

Spin-Orbit Term,  BE (eV) Value, and Scofield σ for Aluminum Kα X-rays (1486 eV, 8.33 Ang)

Overlaps Spin-Orbit Term BE (eV) Value Scofield σ from 1486 eV X-rays IMFP (TPP-2M) in Å
Mg (1s) overlaps Ga (2s) 1301    
  Ga (2p1/2) 1144 11.09 10.7
  Ga (2p3/2) 1116.5 21.40 11.3
S (2p) overlaps Ga (3s) 159 1.13 28.7
  Ga (3p1/2) 108 1.10 29.7
Si (2p) overlaps Ga (3p3/2) 104 2.11 29.7
In (4d) overlaps Ga (3d) 18.62 1.085 31.1

σ:  abbreviation for the term Scofield Photoionization Cross-Section which are used with IMFP and TF to generate RSFs and atom% quantitation

Plasmon Peaks

Ga plasmon 1172.5 eV
Ga plasmon 1158 eV

Auger Peaks

 Intrinsic Plasmon Peak:  ~14 eV above peak max
Expected Bandgap for Ga2O3: 4.8 eV
Work Function for Ga2O3:  ~4.2 eV  (Appl Surfac Sci, 465, p973 (2019))

*Scofield Cross-Section (σ) for C (1s) = 1.0

 Periodic Table 


 

Ga (3p) Spectra from Gallium (Gao) Metal
Fresh exposed bulk produced by extensive Ar+ ion etching

Ga (3p) – raw Ga (3p) – peak-fit (no asymm)
   

 


 

Valence Band Spectrum from Gao Metal
 Fresh exposed bulk produced by extensive Ar+ ion etching

 


 

Plasmon Peaks from Gallium, Gao Metal
 Fresh exposed bulk produced by extensive Ar+ ion etching

Ga (2p) – Extended Range Spectrum Ga (2p) – Extended Range Spectrum – Vertically Zoomed
 Periodic Table 

 

Ga (LMM) Auger Peaks from Ga Metal
 Fresh exposed bulk produced by extensive Ar+ ion etching

Ga Metal – wide range Ga Metal – Expanded
 

Features Observed

  • xx
  • xx
  • xx

 Periodic Table 


 

Artefacts Caused by Argon Ion Etching

Gallium Carbide(s)

can form when ion etched Reactive Metal Surfaces capture
Residual UHV Gases (CO, H2O, CH4 etc)

Argon Trapped in Ga

can form when Argon Ions are used
to removed surface contamination

   

 

Side-by-Side Comparison of
Ga Native Oxide & Gallium Oxide (Ga2O3)
Peak-fits, BEs, FWHMs, and Peak Labels

Ga Native Oxide Ga2O3
Ga (3d) from Ga Native Oxide
Flood Gun OFF
As-Measured, C (1s) at 286.3 eV 
Ga (3d) from Ga2O3 – pressed pellet
Flood Gun ON
Charge Referenced to C (1s) at 285.0 eV

 Periodic Table 

 
Ga Native Oxide Ga2O3
C (1s) from Ga Native Oxide
on Gallium
As-Measured, C (1s) at 286.3 eV (Flood Gun OFF)
C (1s) shifts by 1.8 eV for Native Ga Oxide but Ga BE does not!

C (1s) from Ga2O3 – pressed pellet
Flood Gun ON
Charge Referenced to C (1s) at 285.0 eV
Ga Auger Peaks Overlap C (1s)

 

 

 Periodic Table 

  .
Ga Native Oxide Ga2O3
O (1s) from Ga Native Oxide
on Gallium
As-Measured, C (1s) at 286.3 eV (Flood Gun OFF)

O (1s) from Ga2O3 – pressed pellet
Flood Gun ON
Charge Referenced to C (1s) at 285.0 eV

 

 Periodic Table

 


 
Ga Native Oxide Ga2O3
Ga (KLL) Auger Peaks from Ga Native Oxide
As-Measured, C (1s) at 286.3 eV
Flood Gun OFF

Ga (KLL) Auger Peaks from Ga2O3 –  pressed pellet
Flood Gun ON
Charge Referenced to C (1s) at 285.0 eV


 


Survey Spectrum of Gallium (Ga) Native Oxide
with Peaks Integrated, Assigned and Labelled

 Periodic Table 


 

 

Survey Spectrum of Gallium Oxide (Ga2O3)
with Peaks Integrated, Assigned and Labelled

 

 

 Periodic Table  


 

Overlays of Ga (2p3/2) Spectra for:
Gao metal, Ga Native Oxide and Ga2O

Caution: BEs from Grounded Native Oxides can be Misleading if Flood Gun is ON

 Overlay of Gao metal and Ga Native Oxide – Ga (2p3/2)
Native Oxide C (1s) = 286.3 eV  (Flood gun OFF)
Chemical Shift: 2.9
 Overlay of Gao metal and Ga2O3 – Ga (2p3/2)
Pure Oxide C (1s) = 285.0 eV
Chemical Shift: 2.6
 Periodic Table  Copyright ©:  The XPS Library 

 

Overlay of Ga (2p3/2)
Gao Metal, Ga Native Oxide, & Ga2O3  

 

Overlay of Ga (2p3/2)
Gao Metal & Ga2O3 showing Plasmons and Loss Peaks:   

Features Observed

  • xx
  • xx
  • xx

 Periodic Table 


 

Valence Band Spectra
Gao, Ga2O3 

Gao
Ion etched clean
Ga2O3 – pressed pellet
Flood gun is ON,  Charge referenced so C (1s) = 285.0 eV


Overlay of Valence Band Spectra
for Gao metal and Ga2O3

Features Observed

  • xx
  • xx
  • xx

 Periodic Table 



 

Gallium Man-made Crystals and Chemical Compounds

 

Lanthanum-gallium-silicate Gallium Arsenide – GaAs Gallium Nitride – GaN Gallium Sulfide – GaS

 Periodic Table 



 

 

Six (6) Chemical State Tables of Ga (3d) & (2p3/2) BEs

 

  • The XPS Library Spectra-Base
  • PHI Handbook
  • Thermo-Scientific Website
  • XPSfitting Website
  • Techdb Website
  • NIST Website

 Periodic Table 



 

Notes of Caution when using Published BEs and BE Tables from Insulators and Conductors:

  • Accuracy of Published BEs
    • The accuracy depends on the calibration BEs used to calibrate the energy scale of the instrument.  Cu (2p3) BE can vary from 932.2 to 932.8 eV for old publications 
    • Different authors use different BEs for the C (1s) BE of the hydrocarbons found in adventitious carbon that appears on all materials and samples.  From 284.2 to 285.3 eV
    • The accuracy depends on when the authors last checked or adjusted their energy scale to produce the expected calibration BEs
  • Worldwide Differences in Energy Scale Calibrations
    • For various reasons authors still use older energy scale calibrations 
    • Some authors still adjust their energy scale so Cu (2p3/2) appears at 932.2 eV or 932.8 eV because this is what the maker taught them
    • This range causes BEs in the higher BE end to be larger than expected 
    • This variation increases significantly above 600 eV BE
  • Charge Compensation
    • Samples that behave as true insulators normally require the use of a charge neutralizer (electron flood gun with or without Ar+ ions) so that the measured chemical state spectra can be produced without peak-shape distortions or sloping tails on the low BE side of the peak envelop. 
    • Floating all samples (conductive, semi-conductive, and non-conductive) and always using the electron flood gun is considered to produce more reliable BEs and is recommended.
  • Charge Referencing Methods for Insulators
    • Charge referencing is a common method, but it can produce results that are less reliable.
    • When an electron flood gun is used, the BE scale will usually shift to lower BE values by 0.01 to 5.0 eV depending on your voltage setting. Normally, to correct for this flood gun induced shift, the BE of the hydrocarbon C (1s) peak maximum from adventitious carbon is used to correct for the charge induced shift.
    • The hydrocarbon peak is normally the largest peak at the lowest BE. 
    • Depending on your preference or training, the C (1s) BE assigned to this hydrocarbon peak varies from 284.8 to 285.0 eV.  Other BEs can be as low as 284.2 eV or as high as 285.3 eV
    • Native oxides that still show the pure metal can suffer differential charging that causes the C (1s) and the O (1s) and the Metal Oxide BE to be larger
    • When using the electron flood gun, the instrument operator should adjust the voltage and the XY position of the electron flood gun to produce peaks from a strong XPS signal (eg O (1s) or C (1s) having the most narrow FWHM and the lowest experimentally measured BE. 

 Periodic Table 


Table #1

Ga (3d) Chemical State BEs from:  “The XPS Library Spectra-Base”

C (1s) BE = 285.0 eV for TXL BEs
and C (1s) BE = 284.8 eV for NIST BEs

Element Atomic # Compound As-Measured by TXL or NIST Average BE Largest BE Hydrocarbon C (1s) BE  Source
Ga 31 GaInAs 17.5 eV 18.2 eV 285.0 eV The XPS Library
Ga 31 GaSe 17.6 eV   285.0 eV The XPS Library
Ga 31 Ga – element 18.6 eV   285.0 eV The XPS Library
Ga 31 GaAs (N*16) 18.6 eV 19.7 eV 284.8 eV Avg BE – NIST
Ga 31 GaSb 18.6 eV 19.1 eV 285.0 eV The XPS Library
Ga 31 GaSb (N*4) 18.9 eV 19.0 eV 284.8 eV Avg BE – NIST
Ga 31 GaAs 19.1 eV 19.7 eV 285.0 eV The XPS Library
Ga 31 GaP (N*5) 19.2 ev 19.9 eV 284.8 eV Avg BE – NIST
Ga 31 GaN (N*2) 19.5 eV 19.7 eV 284.8 eV Avg BE – NIST
Ga 31 GaAlAs 19.6 eV   285.0 eV The XPS Library
Ga 31 Ga2Se3 (N*2) 19.7 eV 19.9 eV 284.8 eV Avg BE – NIST
Ga 31 GaP 19.7 eV 20.0 eV 285.0 eV The XPS Library
Ga 31 GaN 20.0 eV   285.0 eV The XPS Library
Ga 31 Ga2O3 (N*5) 20.2 eV 20.7 eV 284.8 eV Avg BE – NIST
Ga 31 Ga-2O3 21.3 eV   285.0 eV The XPS Library
Ga 31 Ga-(OH)3     285.0 eV The XPS Library
Ga 31 Ga-2O     285.0 eV The XPS Library
Ga 31 Ga-Cl3     285.0 eV The XPS Library
Ga 31 Ga-CO3     285.0 eV The XPS Library
Ga 31 Ga-F3     285.0 eV The XPS Library
Ga 31 Ga-S     285.0 eV The XPS Library

Charge Referencing Notes

  • (N*number) identifies the number of NIST BEs that were averaged to produce the BE in the middle column.
  • The XPS Library uses Binding Energy Scale Calibration with Cu (2p3/2) BE = 932.62 eV and Au (4f7/2) BE = 83.98 eV.  BE (eV) Uncertainty Range:  +/- 0.2 eV
  • Charge Referencing of insulators is defined such that the Adventitious Hydrocarbon C (1s) BE (eV) = 285.0 eV.  NIST uses C (1s) BE = 284.8 eV 
  • Note:   Ion etching removes adventitious carbon, implants Ar (+), changes conductivity of surface, and degrades chemistry of various chemical states.
  • Note:  Ion Etching changes BE of C (1s) hydrocarbon peak.
  • TXL – abbreviation for: “The XPS Library” (https://xpslibrary.com).  NIST:  National Institute for Science and Technology (in USA)

 Periodic Table 


Table #2

Ga (2p3/2) & (3d) Chemical State BEs from:  “PHI Handbook”

C (1s) BE = 284.8 eV

 Periodic Table 

Copyright ©:  Ulvac-PHI


Table #3

Ga (2p3/2) and (3d) Chemical State BEs from:  “Thermo-Scientific” Website

C (1s) BE = 284.8 eV

Chemical state Binding energy (eV),
Ga (2p3)
Binding energy (eV)
Ga (3d)
Ga elemental 1116.7 18.7
GaAs 1116.9 19.1
Ga2O3 1118.0 20.5
GaAs native oxide 1117.8 20.3
Ga native oxide 1118.7 20.9

 Periodic Table 

Copyright ©:  Thermo Scientific 


Table #4

Ga (2p3/2) & (3d) Chemical State BEs from:  “XPSfitting” Website

Chemical State BE Table derived by Averaging BEs in the NIST XPS database of BEs
C (1s) BE = 284.8 eV


J.L. Bourque, M.C. Biesinger, K.M. Baines, Dalton Transactions45 (2016) 7678-7696.

 Periodic Table 

Copyright (c) M. Beisinger


Table #5

Ga (2p3/2) & (3d) Chemical State BEs:  “Techdb.podzone.net” Website

 

XPS Spectra – Chemical Shift | Binding Energy
C (1s) BE = 284.6 eV

XPS(X線光電子分光法)スペクトル 化学状態 化学シフト ケミカルシフト

Element Level Compound B.E.(eV) min   max
Ga 3d Ga 18.6 ±0.3 18.3 18.8
Ga 3d Ga2O3 18.7 ±0.3 18.4 18.9
Ga 3d GaAs 19.0 ±0.2 18.8 19.2
Ga 3d AlGaAs 19.0 ±0.3 18.7 19.3
Ga 3d GaP 19.3 ±0.6 18.7 19.9
Ga 2p3/2 Ga 1116.5 ±0.2 1116.3 1116.7
Ga 2p3/2 GaP 1116.8 ±0.3 1116.5 1117.0
Ga 2p3/2 Ga2O3 1117.4 ±0.5 1116.9 1117.8

 

 Periodic Table 



 

Histograms of NIST BEs for Ga (3d) BEs

Important Note:  NIST Database defines Adventitious Hydrocarbon C (1s) BE = 284.8 eV for all insulators.

Histogram indicates:  18.6 eV for Ga metal based on 8 literature BEs Histogram indicates:  20.4 eV for Ga2O3 based on 6 literature BEs

 

Histogram indicates:  19.2 eV for GaAs based on 18 literature BEs

Table #6


NIST Database of Ga (3d) & (2p3) Binding
Energies

NIST Standard Reference Database 20, Version 4.1

Data compiled and evaluated
by
Alexander V. Naumkin, Anna Kraut-Vass, Stephen W. Gaarenstroom, and Cedric J. Powell
©2012 copyright by the U.S. Secretary of Commerce on behalf of the United States of America. All rights reserved.

Important Note:  NIST Database defines Adventitious Hydrocarbon C (1s) BE = 284.8 eV for all insulators.

 

Element Spectral Line Formula Energy (eV) Reference
Ga 3d GaAs/Y 17.00  Click
Ga 3d GaN 17.02  Click
Ga 3d GaN 17.10  Click
Ga 3d GaN 17.76  Click
Ga 3d GaAs/Y 18.00  Click
Ga 3d Ga 18.40  Click
Ga 3d GaP 18.54  Click
Ga 3d GaSb 18.68  Click
Ga 3d GaAs 18.73  Click
Ga 3d GaAs 18.75  Click
Ga 3d GaAs 18.75  Click
Ga 3d GaAs 18.80  Click
Ga 3d GaAs 18.81  Click
Ga 3d GaAs 18.83  Click
Ga 3d GaAs 18.83  Click
Ga 3d GaAs 18.84  Click
Ga 3d GaAs 18.85  Click
Ga 3d GaAs 18.86  Click
Ga 3d GaAs 18.86  Click
Ga 3d GaSb 18.86  Click
Ga 3d In0.53Ga0.47As 18.87  Click
Ga 3d Ga/Si 18.90  Click
Ga 3d GaAs 19.00  Click
Ga 3d GaAs 19.00  Click
Ga 3d GaSe 19.00  Click
Ga 3d GaAs/In0.53Ga0.47As 19.08  Click
Ga 3d GaAs/In0.53Ga0.47As 19.08  Click
Ga 3d GaAs/In0.53Ga0.47As 19.08  Click
Ga 3d GaAs/In0.53Ga0.47As 19.08  Click
Ga 3d In0.53Ga0.47As/GaAs/In0.53Ga0.47As 19.08  Click
Ga 3d In0.53Ga0.47As/GaAs/In0.53Ga0.47As 19.08  Click
Ga 3d Ga 19.10  Click
Ga 3d GaAs 19.10  Click
Ga 3d Ga0.8In0.2As 19.10  Click
Ga 3d GaAs/In0.53Ga0.47As 19.11  Click
Ga 3d GaAs/In0.53Ga0.47As 19.11  Click
Ga 3d GaAs 19.20  Click
Ga 3d Ga0.47In0.53As 19.21  Click
Ga 3d GaAsOx 19.30  Click
Ga 3d GaAs 19.34  Click
Ga 3d GaAs 19.46  Click
Ga 3d GaAs 19.70  Click
Ga 3d Ga2Mo5As4 19.90  Click
Ga 3d GaOOH 20.00  Click
Ga 3d GaAsOx/GaAs 20.04  Click
Ga 3d Ga2O3 20.20  Click
Ga 3d Ga(AsO3)3 20.40  Click
Ga 3d (In,Ga)AsOx 20.50  Click
Ga 3d GaAsOx 20.60  Click
Ga 3d Ga2O3 20.80  Click
Ga 3d Ga2O3 20.90  Click
Ga 3d GaAsO4 20.90  Click
Ga 3d GaAsOx/GaAs 21.29  Click
Ga 3d [Ga768P768O2976(OH)192].[C7H14NF]192 21.80  Click

 

 
Element Spectral Line Formula Energy (eV) Reference
Ga 2p3/2 Ga 1116.50  Click
Ga 2p3/2 Ga 1116.67  Click
Ga 2p3/2 GaAs 1116.80  Click
Ga 2p3/2 GaP 1116.80  Click
Ga 2p3/2 Ga2O3 1116.90  Click
Ga 2p3/2 Ga 1117.00  Click
Ga 2p3/2 Ga 1117.00  Click
Ga 2p3/2 GaAs 1117.00  Click
Ga 2p3/2 GaAs 1117.00  Click
Ga 2p3/2 Ga2O3 1117.50  Click
Ga 2p3/2 GaSe 1117.60  Click
Ga 2p3/2 GaAs 1117.70  Click
Ga 2p3/2 GaN 1117.80  Click
Ga 2p3/2 Ga2O3 1117.80  Click
Ga 2p3/2 Ga2Se3 1118.00  Click
Ga 2p3/2 Ga 1118.10  Click
Ga 2p3/2 CuGa5Se8 1118.10  Click
Ga 2p3/2 Ga2O3 1119.00  Click
 

 Periodic Table 


 

 

Statistical Analysis of Binding Energies in NIST XPS Database of BEs

 

 

 Periodic Table 


 

Advanced XPS Information Section

Expert Knowledge, Spectra, Features, Guidance and Cautions  

for XPS Research Studies on Gallium Materials

 

 


 

Expert Knowledge Explanations

 Periodic Table 


 

Gallium Chemical Compounds

 

Peak-fits and Overlays of Chemical State Spectra

Pure Gallium (Gao):  Ga (3d)
Cu (2p3/2) BE = 932.6 eV
Ga2O3: Ga (3d)
C (1s) BE = 285.0 eV
GaF3:  Ga (3d)
C (1s) BE = 285.0 eV

Features Observed

  • xx
  • xx
  • xx

 Periodic Table 


 

Overlay of Ga (3d) Spectra shown Above

C (1s) BE = 285.0 eV

 

Chemical Shift between Ga and Ga2O3:  2.6 eV
 Chemical Shift between Ga and GaF3:   3.8 eV

 

 Periodic Table 


 

Gallium Oxide (Ga2O3)
3 mm pressed pellet

Survey Spectrum from Ga2O3
Flood gun is ON, C (1s) BE = 285.0 eV
Ga (3d) Chemical State Spectrum from Ga2O3
Flood gun is ON, C (1s) BE = 285.0 eV

 
O (1s) Chemical State Spectrum from Ga2O3
Flood gun is ON, C (1s) BE = 285.0 eV
C (1s) Chemical State Spectrum from Ga2O3
Flood gun is ON, C (1s) BE = 285.0 eV

 
Ga (3s) Chemical State Spectrum from Ga2O3
Flood gun is ON, C (1s) BE = 285.0 eV
Ga (3p) Chemical State Spectrum from Ga2O3
Flood gun is ON, C (1s) BE = 285.0 eV

 
Valence Band Spectrum from Ga2O3
Flood gun is ON, C (1s) BE = 285.0 eV
Auger Signals from Ga2O3
Flood gun is ON, C (1s) BE = 285.0 eV


Energy Loss Peaks for Gallium Oxide, Ga2O3

Energy Loss Peaks for Ga2O3 – Ga (3d), Ga (3p) and Ga (3s)

 


 

Multiplet Splitting Features for
Gallium Compounds

Ga metal – NO Splitting for Ga (3s) Ga2O3 Compound – NO Multiplet Splitting for Ga (3s)

 

Features Observed

  • xx
  • xx
  • xx

 Periodic Table 

 


 

Gallium Chemical Compounds

 

Gallium Fluoride, GaF3

Survey Spectrum  Ga (3d) Spectrum


 
F (1s) Spectrum C (1s) Spectrum


 
Ga (2p3/2) Spectrum Valence Band Spectrum


  .
Ga (Auger) Spectrum  
 
   
   

 Periodic Table 



 

Quantitation Details and Information

Quantitation by XPS is often incorrectly done, in many laboratories, by integrating only the main peak, ignoring the Electron Loss peak, and the satellites that appear as much as 30 eV above the main peak.  By ignoring the electron loss peak and the satellites, the accuracy of the atom% quantitation is in error.

When using theoretically calculated Scofield cross-section values, the data must be corrected for the transmission function effect, use the calculated TPP-2M IMFP values, the pass energy effect on the transmission function, and the peak area used for calculation must include the electron loss peak area, shake-up peak area, multiplet-splitting peak area, and satellites that occur within 30 eV of the main peak.

 

Quantitation from Pure, Homogeneous Binary Compound
composed of Gallium

This section is focused on measuring and reporting the atom % quantitation that results by using:

  • Scofield cross-sections,
  • Spectra corrected to be free from Transmission Function effects
  • A Pass Energy that does not saturate the detector system in the low KE range (BE = 1000-1400 eV)
  • A focused beam of X-ray smaller than the field of view of the lens
  • An angle between the lens and the source that is ~55 deg that negates the effects of beta-asymmetry
  • TPP-2M inelastic mean free path values, and
  • Either a linear background or an iterated Shirley (Sherwood-Proctor) background to define peak areas

The results show here are examples of a method being developed that is expected to improve the “accuracy” or “reliability” of the atom % values produced by XPS.

 Periodic Table 

 


 

 

Flood Gun Effect on Native Oxide of Gallium

 

Native Oxide of Gallium Sheet – Sample GROUNDED

 


 

Native Oxide of Gallium Sheet – Sample Grounded

Electron Flood Gun:  0 Voltage (FG OFF), Min Voltage versus Max Voltage

Ga (3d) O (1s) C (1s)
     
 Periodic Table     

Copyright ©:  The XPS Library


 

Chemical State Spectra from Slow Depth Profile of:
Ga Native Oxide by AES

Native Ga Oxide on Ga ribbon was slowly ion etched using High Energy Resolution conditions to measure Chemical States by Auger

Ga (LMM) O (KLL)
   

 


 

 

Gallium Alloys

   
XxCu XxCu
 Periodic Table   
XxCu XxCu

 

Copyright ©:  The XPS Library 

 



 

XPS Facts, Guidance & Information

 Periodic Table 

    Element   Gallium (Ga)
 
    Primary XPS peak used for Peak-fitting:   Ga (2p)  or Ga (3d)  
    Spin-Orbit (S-O) splitting for Primary Peak:   Spin-Orbit splitting for “p” orbital, ΔBE = 26.9 eV
 
    Binding Energy (BE) of Primary XPS Signal:   1117 eV  for Ga (2p3/2)
18 eV for Ga (3d)
 
    Scofield Cross-Section (σ) Value:   Ga (2p3/2) =21.40      Ga (2p1/2) =11.09
Ga (3d) =1.085     Ga (3p) =3.21
 
    Conductivity:   Ga resistivity =  
Native Oxide suffers Differential Charing
 
    Range of Ga (2p) Chemical State BEs:   xx – xx eV range   (Ga to GaF2)  
    Signals from other elements that overlap
Ga (2p) Primary Peak:
  xx (xx)  
    Bulk Plasmons:   ~xx eV above peak max for pure  
    Shake-up Peaks:   xx  
    Multiplet Splitting Peaks:   xx  

 

 

General Information about
XXX Compounds:
  xx  
    Cautions – Chemical Poison Warning  

xx 

 

Copyright ©:  The XPS Library 

 Periodic Table 



 

Information Useful for Peak-fitting Ga (3d)

  • Ga (3d) FWHM (eV) of Pure Ga metal :  ~0.6 eV using 50 eV Pass Energy after ion etching:
  • Ga (3d) FWHM (eV) of Ga2O3 xtal:  ~1.3 eV using 50 eV Pass Energy  (before ion etching)
  • Binding Energy (BE) of Primary Signal used for Measuring Chemical State Spectra:  18 eV for Ga (3d) with +/- 0.2 uncertainty
  • List of XPS Peaks that can Overlap Peak-fit results for Ga (3d):  xxxx

 Periodic Table 


 

General Guidelines for Peak-fitting XPS Signals

  • Typical Energy Resolution for Pass Energy (PE) setting used to measure Chemical State Spectra on Various XPS Instruments
    • Ag (3d5/2) FWHM (eV) = ~0.95 eV for PE 50 on Thermo K-Alpha
    • Ag (3d5/2) FWHM (eV) = ~1.00 eV for PE 80 on Kratos Nova
    • Ag (3d5/2) FWHM (eV) = ~0.95 eV for PE 45 on PHI VersaProbe
  • FWHM (eV) of Pure Elements: Ranges from 0.4 to 1.0 eV across the periodic table
  • FWHM of Chemical State Peaks in any Chemical Compound:  Ranges from 1.1 to 1.6 eV  (in rare cases FWHM can be 1.8 to 2.0 eV)
  • FWHM of Pure Element versus FWHM of Oxide:  Pure element FWHM << Oxide FWHM  (e.g. 0.8 vs 1.5 eV, roughly 2x)
  • If FWHM Greater than 1.6 eV:  When a peak FWHM is larger than 1.6 eV, it is best to add another peak to the peak-fit envelop.
  • BE (eV) Difference in Chemical States: The difference in chemical state BEs is typically 1.0-1.3 eV apart.  In rare cases, <0.8 eV.
  • Number of Peaks to Use:  Use minimum. Do not use peaks with FWHM < 1.0 eV unless it is a or a conductive compound.
  • Typical Peak-Shape:  80% G: 20% L,   or Voigt : 1.4 eV Gaussian and 0.5 eV Lorentzian
  • Spin-Orbit Splitting of Two Peaks (due to Coupling):  The ratio of the two (2) peak areas must be constrained.

Notes:

  • Other Oxidation States can appear as small peaks when peak-fitting
  • Pure element signals normally have asymmetric tails that should be included in the peak-fit.
  • Gaseous state materials often display asymmetric tails due to vibrational broadening.
  • Peak-fits of C (1s) in polymers include an asymmetric tail when the energy resolution is very high.
  • Binding energy shifts of some compounds are negative due to unusual electron polarization.

 Periodic Table 


 

Contaminants Specific to Gallium

  • Gallium develops a thick native oxide due to the reactive nature of clean Gallium .
  • The native oxide of Ga Ox is 5-9 nm thick.
  • Gallium thin films often have a low level of iron (Fe) in the bulk as a contaminant or to strengthen the thin film
  • Gallium forms a low level of carbide when the surface is ion etched inside the analysis chamber

 

Commonplace Contaminants

  • Carbon and Oxygen are common contaminants that appear on nearly all surfaces. The amount of Carbon usually depends on handling.
  • Carbon is usually the major contaminant.  The amount of carbon ranges from 5-50 atom%.
  • Carbon contamination is attributed to air-borne organic gases that become trapped by the surface, oils transferred to the surface from packaging containers, static electricity, or handling of the product in the production environment.
  • Carbon contamination is normally a mixture of different chemical states of carbon (hydrocarbon, alcohol or ether, and ester or acid).
  • Hydrocarbon is the dominant form of carbon contamination. It is normally 2-4x larger than the other chemical states of carbon.
  • Carbonate peaks, if they appear, normally appear ~4.5 eV above the hydrocarbon C (1s) peak max BE.
  • Low levels of carbonate is common on many s that readily oxidize in the air.
  • High levels of carbonate appear on reactive oxides and various hydroxides.  This is due to reaction between the oxide and CO2 in the air.
  • Hydroxide contamination peak is due to the reaction with residual water in the lab air or the vacuum.
  • The O (1s) BE of the hydroxide (water) contamination normally appears 0.5 to 1.0 eV above the oxide peak
  • Sodium (Na), Potassium (K), Sulfur (S) and Chlorine (Cl) are common trace to low level contaminants
  • To find low level contaminants it is very useful to vertically expand the 0-600 eV region of the survey spectrum by 5-10X
  • A tiny peak that has 3 or more adjacent data-points above the average noise of the background is considerate to be a real peak
  • Carbides can appear after ion etching various reactive s.  Carbides form due to the residual CO and CH4 in the vacuum.
  • Ion etching can produce low oxidation states of the material being analyzed.  These are newly formed contaminants.
  • Ion etching polymers by using standard Ar+ ion guns will destroy the polymer, converting it into a graphitic type of carbon

 Periodic Table 


 

Data Collection Guidance

  • Chemical state differentiation can be difficult
  • Collect principal Ga (2p) peak as well as Ga (3d).
  • Long time exposures (high dose) to X-rays can degrade various polymers, catalysts, high oxidation state compounds
  • During XPS analysis, water or solvents can be lost due to high vacuum or irradiation with X-rays or Electron flood gun
  • Auger signals can sometimes be used to discern chemical state shifts when XPS shifts are very small

 Periodic Table 


 

Data Collection Settings for Gallium (Ga)

  • Conductivity:  Gallium readily develops a native oxide that is sensitive to Flood Gun – Differential Charging Possible – float sample recommended
  • Primary Peak (XPS Signal) used to measure Chemical State Spectra:  Ga (3d) at 18 eV and Ga (2p3) at 1116 eV
  • Recommended Pass Energy for Measuring Chemical State Spectrum:  40-50 eV    (Produces Ag (3d5/2) FWHM ~0.7 eV)
  • Recommended # of Scans for Measuring Chemical State Spectrum:  4-5 scans normally   (Use 10-25 scans to improve S/N)
  • Dwell Time:  50 msec/point
  • Step Size:  0.1 eV/point   (0.1 eV/step or 0.1 eV/channel)
  • Standard BE Range for Measuring Chemical State Spectrum:  10 – 30 eV
  • Recommended Extended BE Range for Measuring Chemical State Spectrum:  0 to 110 eV
  • Recommended BE Range for Survey Spectrum:  -10 to 1,100 eV   (above 1,100 eV there are no useful XPS signals, except for Ge and Ga)
  • Typical Time for Survey Spectrum:  3-5 minutes for newer instruments, 5-10 minutes for older instruments
  • Typical Time for a single Chemical State Spectrum with high S/N:  5-10 minutes for newer instruments, 10-15 minutes for older instruments 

 Periodic Table 


 

Effects of Argon Ion Etching

  • Ion etching can produce low oxidation states of the material being analyzed.  These are newly formed contaminants.
  • Ion etching polymers by using standard Ar+ ion guns will destroy the polymer, converting it into a graphitic type of carbon

 Periodic Table 

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Gas Phase XPS or UPS Spectra
 

 
     
     
     
     
     
     
     
     
     
 
 
 
 

 

Chemical State Spectra from Literature
 
Spectra from Thermo Scientific Website
 
 
 



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